Combination flotation-settling unit



May 26, 1959 FISCHER 2,888,139

COMBINATION FLOTATION-SETTLING UNIT Filed April 25. 1955 2 Sheets-Sheet 1 A. J. FISCHER May 26, 1959 COMBINATION FLOTATION-$ETTLING UNIT 2 Sheets-Sheet 2 Filed April 25. 1955 INVENTOR. ANTHONY J. FlSCHER United States Patent COMBINATION FLOTATION-SETTLING UNIT Anthony J. Fischer, Manhasset, N.Y., assignor to Dorr- Oliver Incorporated, Stamford, Conn., a corporation of Delaware Application April 25, 1955, Serial No. 503,660

Claims. (Cl. 210221) This invention relates to an apparatus for the treatment of liquid wastes such as sanitary sewage and industrial wastes which contain solid particles and immiscible liquid droplets, and, more particularly, to a dual purpose apparatus therefor.

The treatment of sewage, industrial wastes, and similar polluted liquids may be classified into two main groups. The first may be regarded as consisting of those that act solely as mechanical or physical separating means for the removal of solid and immiscible liquid droplets and include devices such as bar racks, screens, gravity settling clarifiers, and flotation devices. The second group includes those devices which exert not only a physical function but also a biochemical one. This group may be exemplified by installations such as trickling filters, and activated sludge aeration and contact tanks. Generally speaking, the devices of the first group may be used alone to accomplish so-called primary treatment, or they may be used in conjunction with devices of the second group to accomplish complete treatment. This invention is concerned primarily with an improved design for one of the classes of devices in the primary treatment group, or, more particularly, that class in which flotation of undissolved impurities (which term as used herein shall be deemed to include both solids and immiscible liquid droplets) constitutes one of the major functions of the apparatus.

Flotation devices, as presently used, generally comprise a detention tank equipped with scum skimmer means together with means for introducing, or otherwise releasing gas bubbles for upward migration through the liquid contained therein. While some of the impurities present in the liquid have a specific gravity less than that of water and will consequently tend to rise to the surface naturally, the gas introduced acts to accelerate this tendency, and, further, to bring about the flotation of heavier solids which would otherwise tend to settle or remain suspended. This function of the gas bubbles is, of course, accomplished by reason of the fact that the bubbles adhere and otherwise attach themselves to the impurities and impart bouyancy thereto. In addition to this bouyant effect, the bubbles also tend to entangle the impurities in the foam which forms on the surface, and thus to retain them there until removed.

Since flotation devices, where used, constitute a major step in the waste treatment process, any shut-down of the flotation apparatus will bring about a major deterioration in the quality of the plant eflluent. In the past, whenever the bubble infusion means have ceased functioning for'one reason or another, the treatment station was, by reason of the fact that its design was based solely on flotation efliciency, rendered essentially namely the path taken by the flow in the course of transit through the unit. In flotation devices it is, of course, desirable to maintain the liquid stream being treated in the form of a moving sheet flowing close to the surface of the main liquid body during the period when active contacting of the impurities with the bubbles is occurring. This design characteristic is desirable in order that the distance travelled by the bouyed-up impurities be minimized. Following the active bubble-impurity contacting period, however, it is desirable that the liquid stream be removed from the region of the surface in order to avoid turbulence and the washing out of the floated material with the efiluent of the unit. As a result, the efliuent discharge means used in flotation devices generally take the form of discharge ports or pipes drawing treated liquid from well below the surface of the liquid body.

In settling units on the other hand, it is highly desirable that as much of the tank volume as possible be utilized by the liquid in flowing through the tank. Generally speaking it has been found that in circular tanks utilizing central feedwells, the maximum practical volumetric efliciency can be attained by causing the influent to enter the treatment tank in such manner that the liquid will, during treatment, move from the lower central portion of the tank to efliuent collection and discharge means located at or near the surface.

It may then be seen that in circular units, whereas flotation treatment calls for the generally horizontal movement of influent for a distance along the surface and then downwardly to collection means at a level materially below that of the surface, the hydraulic requirements of settling call for liquid movement in a generally upward direction from a region in the lower portion of the tank to collection means at or near the surface. These two requirements are of course quite incompatible and, practically speaking, units as designed at present for effective flotation cannot be made to-operate as eflective settling devices and vice versa.

This invention has as its principal object an improved liquid waste treatment apparatus capable of functioning alternately as an effective flotation device and as an effective settling device. More particularly, this invention achieves the stated object through the provision of means whereby raw flow to be treated may be directed radially outward from an influent point centrally located at or near the surface of a cylindrically shaped body of liquid undergoing treatment to collection by means located well below the said surface, or, alternately directed downward toward the central bottom portion of the said body whence it migrates to collection by means located at or near the said surface.

These and other objects are achieved, in one embodiment, by providing the terminal section of the treatment tank influent pipe with a plurality of moveable vanes, said vanes being so mounted that they can be placed either into a position whereby influent flow is caused to move radially and horizontally away from the center and at a level close to that of the surface of the tank contents, or, alternately, the said vanes may be positioned to cause influent flow to pass downwardly toward the bottom central portion of the tank, whence it flows laterally and upwardly to discharge. In order, however, to attain the optimum hydraulic characteristics outlined hereinabove, additional means are provided for altering the level at which treated liquid is withdrawn from the tank. Thus, in the embodiment shown in the drawing, removable efiluent collecting pipes are mounted in openings in the bottom of the efiiuent channel, said pipes being in full downwardly extended position when the unit is operating as a flotation device, and drawing treated liquid from the level of the pipe bottoms. When the unit is operating as a settling device, the pipes are removed and treated liquid is withdrawn at the level of the elfluent channel bottom.

In another embodiment, the same ends are achieved by utilizing a vertically positionable feedwell in place of the moveable vanes. In this embodiment, the influent is caused to flow radially and horizontally away from the center and at a level close to that of the surface either by lowering the feedwell to a point where its upper edge is submerged and influent enters the tank proper by passage over the said edge, or by lifting the feedwell completely clear of the liquid body and allowing upwardly entering influent to pass laterally directly into the tank proper. Downward movement of influent toward the tank bottom is induced by placing the feedwell into a position in which its upper edge is well above the level of the surface of the liquid tank, while its lower edge is submerged. Raw influent would thereby be forced to move in a downwardly direction towards the tank bottom.

While the description contained herein relates primarily to circular units, it should be noted that the fundamental principles of this invention are equally applicable to rectangular, longitudinal flow tanks in which the liquid to be treated enters at one end, traverses the length of the tank, and is withdrawn at or near the other end. In such application, the feedwell arrangement described herein is replaced by a vaned or positionable baffle disposed at or near the influent end of the unit, said baffle being adapted to produce either surface proximate, flotation facilitating movement of the influent flow, or an initially downwardly directed movement whereby the flow is caused to pass through the unit, during settling treatment, with relatively uniform cross-sectional flow distribution and, consequently, maximum tank volume utilization. The treated liquid collecting means is disposed at or near the efiluent end, and, in a manner analogous to that described for circular units, is adapted to draw treated liquid from a level remote from the surface during flotation operation, and from a level proximate the surface during settling operation.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims, or of forms that are their functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by those claims.

In the drawings:

Figure 1 is a schematic representation of this invention as used in flotation treatment.

Figure 2 is a schematic representation of this invention as used in settling treatment.

Figure 3 is a cross-sectional elevational view of an apparatus incorporating this invention in one of its embodiments.

Figure 4 is a sectional view of the Figure 3 apparatus taken along section 4--4.

Figures 5 and 6 are schematic representations of an alternate feedwell structure which may be used to effect the objects of this invention; Figure 5 illustrating its flotation facilitating position and Figure 6 its settlement facilitating position.

Figure 1 illustrates the flow pattern achieved when the influent control means is positioned to cause influent flow to pass radially into the treatment unit in order to facilitate flotation of impurities. The basic apparatus elements shown comprise a treatment tank with bottom 109 and peripheral wall 110 for containing a body of liquid undergoing treatment; influent conduit 101, for introducing the liquid in an initially upwardly direction in the upper central region of the unit; feedwell 102 with positionable vanes 103 (shown in this figure in their open position) efliuent channels 111 with efiluent discharge pipe 114 and removable efliuent collecting pipe 104 passing through openings 120 in the eflluent channel bottom; a scum skimmer arm 106 with skimmer blade 112, a scum trough 107, with scum chamber 108 and scum discharge pipe and settled solids sump 116 with discharge pipe 117. Waste liquid enters the unit initially by way of conduit 101, whence it passes in an upwardly direction into feedwell 102. With vanes 103 in their open, radial flow inducing position, the influent passes radially and horizontally away from the center of the unit, flowing at a level approximate to the liquid surface 113. Having passed a distance from the center, the stream is caused, by the draw-down effect of the effiuent collecting pipes 104, to change direction and move generally downward toward, and into the open ends of the said collecting pipes. Passing upwardly through the collecting pipes, the treated liquid enters eflluent channel 111 and passes thence to discharge from the unit by way of pipe 114. It should be noted, that during the entire course of its passage from the feedwell to the collecting pipes, the liquid Waste being treated is subjected to the flotation promoting action of rising gas bubbles 118, said bubbles having been introduced with the feed, by dilfusion directly into the tank, or otherwise. Since the liquid stream moves in a sheet-like manner across the upper portion of the tank during treatment, it will be observed that the opportunity for the solids to which the bubbles have become attached to be disengaged therefrom is minimized. Scum or foam containing the floated matter is expeditiously removed from the surface by the skimmer arm 106 with skimming blade 112, and is discharged into scum trough 107, whence it passes to chamber 108 and is discharged by way of pipe 115. High density rapidly settling solids relatively unaffected by the flotation process are removed from the tank bottom by way of sump 116 with discharge pipe 117.

Figure 2 illustrates the flow characteristics of the unit when utilized as a settling tank. All apparatus elements are identical with those of Figure 1, except that the efliuent collecting pipes 104 have been removed, and the feedwell vanes 103 have been moved to their closed position. Consquently, waste liquid entering the feedwell 102 is forced to move in a generally downward direction toward the central lower portion of the unit, whence it moves laterally and upwardly toward and through openings 120 in the bottom of the eflluent channel 111, said openings being those through which the effluent collecting pipes passed in the Figure 1 application. Treated liquid entering channel 111 is again discharged by way of pipe 114. Solids removed by settlement pass into sump 116, and are discharged by pipe 117. While the primary object of operation according to the Figure 2 flow pattern is effective settling, some light material will generally float. These materials are removed from the surface 113 by skimmer arm 106 with blade 112 and deposited into trough 107, whence they pass by gravity to chamber 108 and are discharged by means of pipe 115. In the Figure 2 method of operation, settling is enhanced by reason of the low velocities achieved through a utilization of a large part of the tank volume as indicated by the directional arrows.

Figures 3 and 4 illustrate an actual apparatus embodiment incorporating the features of this invention. The unit comprises a tank with bottom 18 and peripheral wall 17 for containing a body of liquid undergoing treatment, raw feed entering said tank by way of influent pipe 11 with valve 46. In the particular embodiment shown, gas is introduced to the influent by diverting a portion of the flow passing through influent pipe 11 into pipe 34 with valves 35 leading to pump P which impells said diverted liquid through an aeration means which comprises, in this case, a venturi type aspirator 37, with valved air intake 38. Aerated liquid leaving the aerator is conducted back to influent pipe 11 by way of pipe 47 with valve 36, for mixing with the remainder of the influent flow.

Influent pipe 11 discharges into rotatable riser column 12 whence it passes upwardly into the zone defined by annular feedwell 13, said annular feedwell being disposed in the upper central portion of the treatment tank and fitted with positionable vanes 14 rotatable on horizontal axes. Handles 15 are attached to vanes 14 for manual placement of the vanes into the desired position. Waste liquid, after treatment in the unit, passes into elfluent channel 22 either by way of removable eflluent pipes 21 with lifting loops 25 or by way of openings 45, depending on the character of the treatment as hereinafter described. Eflluent channel 22 discharges by way of pipe 23 with valve 24 leading to disposal or further treatment. Floating material is transported by rotating skimmer arms 28 with skimmer blade 29 into scum trough 30, through which it passes by gravity into scum chamber 31, whence it is discharged to Waste by way of pipe 30 with valve 33. Solids settling to the bottom of the unit are collected by rotating scraper assembly 19 with blades 20, and deposited into annular sludge sump 39 whence they are discharged to waste by way of pipe 41 with valve 42. Sludge thickening blades 40, also supported and rotated by scraper assembly 19 are provided in the sludge sump.

Motive power for actuating the roating scum skimmer arm 28 and sludge scraper assembly 19 is provided by drive means 26 mounted on supporting member 43 which rests, in the embodiment illustrated, on the peripheral tank wall 17. Torque shaft 27 serves, not only to support and rotate skimmer arm 28, but, additionally, through members 49, to support and rotate riser column 12 with scraper assembly 19 dependent therefrom. Steady-bearings 48 serve to maintain the vertical axial alignment of rotating riser column 12.

When operating as a flotation device, the embodiment illustrated in Figures 3 and 4 functions as follows. Prior to entry into the unit, a portion of the liquid waste to be treated is diverted by way of pipe 34 with valve 35 into pump P which impells said diverted liquid into an aeration unit of the aspirator type 37 which causes air drawn in through valved pipe 38 to be intimately dispersed therein primarily in the form of minute bubbles. The liquid so aerated passes back to influent pipe 11 by way of pipe 47 with valve 36, re-entering said influent pipe at a point downstream from the original point of diversion, and becoming intimately mixed with the undiverted portion of the flow. Influent pipe 11, terminates in the lower central portion of the tank, and discharges upwardly into a rotatable riser column 12 annularly surrounding the terminus of the said influent pipe and functionally isolating the said terminus from the tank contents. Moving upwardly through the riser column, the gas-bearing influent liquid passes into a zone in the upper portion of the tank contents defined by the partially submerged feedwell 13, bearing, in vertical alignment, a plurality of positionable vanes 14. For purposes of flotation as hereinabove explained, the vanes are in their open position as shown. The gas-bearing liquid emerging from the riser 12 takes the course of least resistance, and, consequently, passes laterally and radially through the open vane ports whence it moves, in a flowing sheet-like manner, and at a level proximate to the surface of the tank liquid contents, toward the periphery of the tank. During the course of the movement of the waste liquid radial- 1y across the tank, the gas bubbles present attach themselves to impurities also present in the said liquid, and act to buoy them up to the surface where they form a floating layer of scum or foam.

Having thus been stripped of a major portion of its impurities, it becomes desirable to remove the liquid from the region on the surface of the tank contents in order that interference with the flotation processes be minimized, and to avoid the possibility of drawing floating material off with the efiluent. For this reason, effluent collecting pipes 21 are provided, extending downwardly through openings 45 in the bottom of the efiluent channel 22, said pipes being held in position by flanges 51 resting on that portion of the eflluent channel bottom adjacent said openings 45. Treated liquid passes downwardly from the surface in the region of the periphery, and enters the efiluent collecting pipes 21 by way of the bottoms thereof. Rising through the said pipes, the liquid flows into efliuent channel 22 whence it is discharged by way of pipe 23 with valve 24. While the unit, when operated in this manner, will function primarily as a flotation device, it should be noted that some high density solids which resist the flotational effect of the bubbles will generally be present and will deposit on the bottom. Floating surface materials, and settled bottom solids' are removed separately by the method and means hereinabove described.

In the event that the aeration means be shut down, or if, for any other reason, it becomes desirable or imperative to discontinue flotation treatment, it is a unique characteristic of this apparatus that it is operable alternately as an efficient settling device. To effect this end, means are provided both for inducing an initially downward movement of the influent stream from the feedwell zone into the main body of liquid undergoing treatment, and for withdrawing treated liquid from the region of the tank periphery at a level proximate to the surface. In the illustrative embodiment shown in Figures 3 and 4, these means take the form, respectively, of the positionable feedwell vanes 14 which, for purposes of settling efficiency, are placed in closed position 44 shown by dash lines in Figure 4, and the removable eflluent collecting pipes 21 fitted with loops 25 for manual, vertically upward withdrawal of said pipes from their flotation enhancing position in opening 45 disposed in the bottom of effluent launder 22.

With aerator isolating valves 35 and 36 closed and pump P stopped, waste liquid reaches the region of the feedwell 13 without the presence of flotation inducing gases. Feedwell vanes 14 also being closed for settling operation, the influent is forced to assume a generally downward direction of flow, its downward momentum being sufficient to carry the main stream into the lower portion of the main body of liquid undergoing treatment (see Figure 2). Since following the removal of pipes 21, the region of efiluent collection has now been moved to the upper peripheral portion of the tank, the liquid undergoing treatment will tend to migrate generally laterally and upwardly to removal through ports 45, whence it enters effluent channel 22, and is discharged to waste or further treatment by way of pipe 23 with valve 24. It may be noted that, as indicated again in Figure 2, this allows for greatly increased utilization of tank volume, with consequent lower velocities and improved settling characteristics. While operation by this method has, as its primary object, the efficient settlement of impurities, some light material may, nevertheless, rise to the surface to form a floating scum layer. These floating scum materials, and settled bottom solids are separately removed by the methods and means hereinabove described.

Figures 5 and 6 illustrate, schematically, a second means for effecting flotation enhancing or, alternately, settlement enhancing flow conditions. In this case a vaneless feedwell 75 is disposed annularly about the riser column 12, said feedwell being adapted, however, to being raised or lowered. In its lowered position, shown in Figure 5, influent emerging upwardly from the riser column 12 passes radially and laterally over the upper edge of the feedwell 75 toward the tank periphery in a manner analogous to that induced by the open vane position of the Figures 3 and 4 embodiment. With feedwell 75 in its raised position as shown in Figure 6, the influent is directed initially downward in a manner analogous to that induced by the closed vane position of the Figures 3 and 4 embodiment. The remainder of the apparatus and methods of operation are identical with that of the Figures 3 and 4 embodiment as herein described.

I claim:

1. Apparatus for the treatment of impure liquid for the removal of suspended material therefrom comprising a tank with a bottom and side walls for containing a body of the liquid undergoing treatment, an impure liquid feed means, treated liquid collecting means and treated liquid discharge means, floating material collecting means and floating material discharge means, and settled material collecting means and settled material discharge means, and a dual position influent flow directing means in hydraulically cooperative relationship with the said feed means, and adapted for placement into surface-proximate flow directing position whereby flotation of impurities in the remainder of the tank is facilitated, and for placement into a position whereby the influent how is directed in an initially downwardly direction whereby settling in the remainder of the tank is facilitated, said treated liquid collecting means also being positionable whereby, at such times as the influent flow directing means is in its surface-proximate flow directing position, the said treated liquid collecting means draws liquid from a level remote from the surface in order to avoid interference with the flotation process, while at such times as the influent flow directing means is in its initially downward influent flow directing position, the said treated liquid collecting means draws liquid from a level near the surface in order to permit maximum utilization of tank volume for settlement.

2. Apparatus according to claim 1, wherein the said positionable treated liquid collecting means comprises an eflluent channel functionally remote from the said impure liquid feed means, said channel being in hydraulic communication with the body of liquid undergoing treatment by way of a plurality of openings in the bottom of the said channel, said collecting means being further adapted to receive removable pipes extending downwardly through each of the said openings in the channel bottom to a level remote from the surface of the liquid body undergoing treatment for drawing liquid therefrom during such time as the influent flow directing means is in its flotation facilitating, surface-proximate flow directing position; said opening being so disposed that when said pipes are withdrawn, liquid enters the said channel by way of said openings from a level proximate the surface of the liquid body.

3. Apparatus according to claim 1, wherein there are provided additional means for producing an evolution of gas bubbles within the said body of liquid undergoing treatment, said bubbles being effective in causing, by attachment to the materials suspended in the liquid, a rapid rise of said materials to the surface of said liquid body, whence they are removed by said floating material collecting means.

4. Apparatus according to claim 3, wherein the said means for producing an evolution of gas bubbles comprises means for saturating the influent liquid feed with gas at greater than atmospheric pressure, whereby, upon the passage of the liquid feed into the said body of liquid undergoing treatment, at the surface whereof atmospheric pressures prevail, the gas will pass from solution and emerge in the form of bubbles.

5. The apparatus according to claim 3, wherein the said means for producing an evolution of gas bubbles comprises the introducing of gas in finely sub-divided form into at least a portion of the influent feed, said bubbles, upon entry into the said body of liquid undergoing treatment with the influent liquid, tending to rise through the said body.

6. Apparatus according to claim 1, wherein the said sidewalls are circular in horizontal cross section, said impure liquid feed means being adapted to submergedly and upwardly discharge liquid to be treated into the upper central portion of the body of liquid undergoing treatment, and wherein the said flow directing means in hydraulically cooperative relationship with the said feed means comprises the plurality of movable, two-position vanes, said vanes being adapted for placement into outwardly radial flow inducing position whereby flotation of impurities is facilitated, and into a position inducing an initially downwardly directed movement of the influent flow thereby causing the said influent to enter the main portion of the body of liquid undergoing treatment at a level below that of the said treated liquid collecting means whereby settlement of impurities is facilitated.

7. Apparatus according to claim 6, wherein the said plurality of movable two-position vanes are pivoted on vertical axes lying within a cylindrical section disposed annularly about the said feed inlet terminus.

8. Apparatus according to claim 6, wherein the said feed means comprises a riser column vertically and axially disposed within said cylindrical tank and extending from the bottom thereof to a level below the surface of the liquid body contained in the said tank, said riser column discharging liquid to be treated into a zone defined by an annularly disposed feedwell wherein are mounted, on vertical axes, the said movable flow directing, twoposition vanes.

9. Apparatus according to claim 1, wherein the said sidewalls are circular in horizontal cross section, said impure liquid feed means being adapted to submergedly and upwardly discharge liquid to be treated into the upper central portion of the body of liquid undergoing treatment, and wherein the said flow directing means in hydraulically cooperative relationship with the said feed means comprises a vertically positionable open ended feedwell annularly surrounding the terminus of the said feed means, said feedwell being adapted, in its lowered position, to induce influent flow to pass over the upper edge of the feedwell and to move thence generally radially outward, whereby the flotation of impurities is facilitated, and in its raised position to cause the said influent flow to pass in a generally downwardly direction through the feedwell toward the bottom of the said tank, whereby the settling of impurities is facilitated.

10. Apparatus for the treatment of impure liquid for the removal of suspended material therefrom, a tank with a bottom and a peripheral wall for containing a body of the liquid undergoing treatment, an inlet conduit with a vertical terminal section centrally disposed within the tank and adapted to discharge infiuent liquid upwardly into a partially submerged annular feedwell, laterally surrounding the terminus of the said inlet conduit, mechanically impelled sludge raking means for transporting the material settling from the liquid toward the center of the tank bottom, a central bottom sump adapted to receive the material so raked and to discharge it from the tank, mechanically impelled floating scum skimming means, a scum chamber adapted to receive the scum collected by said scum skimming means and to discharge it from the tank, treated liquid collection means comprising a peripheral eflluent channel and associated efiluent discharge means and two-position, movable vanes associated with the said feedwell, said twoposition vanes being adapted, in their closed position, to cause all influent flow to pass into the liquid body in a generally downward direction and, in their open position, to cause the liquid influent to pass generally radially outward into the liquid body at a level proximate the surface of the said body; said apparatus being further characterized by the presence of a plurality of openings in the bottom of the said peripheral eflluent channel which openings constitute hydraulic communication means between the channel and that portion of the liquid body adjacent the surface thereof, and through which openings treated effluent passes from the said liquid body into the channel at such times as the said two-position vanes are in their closed position, together with a removable pipe adapted for positioning within said openings to extend downwardly therethrough to a level Within the body of liquid undergoing treatment remote from the surface thereof, to provide hydraulic communication between the said channel and said remote level whereby treated liquid is caused to pass into said channel from said level at such times as the said two-position vanes are in their open position.

References Cited in the file of this patent UNITED STATES PATENTS 2,205,199 Hubbell et al. June 18, 1940 2,375,282 Clemens May 8, 1945 2,695,710 Gibbs Nov. 30, 1954 

